Method for finishing crude benzene by treating with sulfuric acid, neutralizing and distilling in the presence of a flux oil



July 3, 1956 R. M. LOVE 2,753,387

METHOD FOR FINISHING CRUDE BENZENE BY TREATING WITH SULFURIC ACID, NEUTRALIZING AND DISTILLING IN THE PRESENCE OF A FLUX OIL Filed Jan. 28, 1953 19 SETTLER CRUDE BENZE/VE sums:

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I HEAT EXCHA/MEfi 54 2 ---aarrous INVENTOR. Robert M. L 0 ve,

A TTORNEX METHOD FOR FINISHING CRUDE BENZENE BY TREATING WITH SULFURIC ACID, NEUTRALIZ- ING AND DllSTILLllNG IN THE PRESENCE OF A FLUX 01L Robert M. Love, Baytown, Tern, assignor, by mesne assignments, to Esso Research and Engineering Company, Elizabeth, N. J., a corporation of Delaware Application January 28, 1953, Serial No. 333,681

3 Claims. (Cl. 260674) The present invention is directed to a method for finishing a crude benzene to obtain a high purity product.

Crude benzene such as that obtained from the extractive distillation of virgin, hydroformed or cracked naphthas in the boiling range of 1504.50" F. usually contains impurities having the same boiling range as the benzene such as olefins, diolefins, paraflins and sulfur compounds. These impurities cannot be separated from the benzene by normal extractive distillation processes and are present in such amounts that the crude benzene will not pass specifications for a high purity benzene. An example of a specification for a high purity nitration grade benzene is the American Society for Testing Materials, Specification D 835-50 and an example of a specification for a high purity industrial grade benzene is the American Society for Testing Materials, Specification D 836-50. By way of example, it may be stated generally that the crude benzene contains approximately 95% benzene and 5% impurities while it is desirable that a high purity benzene have a total amount of impurities less than .5%.

The method of the present invention wherein a crude benzene feed stock is treated to obtain a high purity benzene product is described in conjunction with the drawing in which the sole figure is in the form of :1 diagrammatic flow sheet.

In the process of the present invention a crude benzene feed stock containing approximately 95% benzene and 5% impurities of which the major portion are olefinic materials is charged through inlet line 11 to which is added strong sulfuric acid by inlet line 32, the admixture of crude benzene and sulfuric acid being discharged into acid treater 13. The strong sulfuric acid should have a concentration within the range of 90% to 100% and is added in amounts within the range of 5 to 50 pounds per barrel of crude benzene. In treater 13 settling takes place so that there is an upper layer of acid treated benzene and a lower layer of resultant acid sludge. The sludge is withdrawn through outlet line 14 and the acid treated benzene is withdrawn through outlet line 1:; and is heated in heat exchanger 16 to a temperature in the range of 250-350 F. The heated oil is passed into line 17 where it is admixed with an aqueous solution of alkali metal hydroxide introduced through line 18, the admixture of the benzene and alkali metal hydroxide passing into settling vessel 19.

It is essential that the benzene remain in intimate contact with the caustic at a temperature in the range of ZEN-350 F. for at least 20 minutes. The caustic used may have a molarity within the range or l-lO. The benzene and caustic are maintained in the liquid phase and, accordingly, a sufficient pressure must be maintained on the mixture to prevent vaporization. The admixture of the benzene with the solution of alkali metal hydroxide occurs in line 17 and contact occurs for at least 20 minutes with the temperature maintained in the range of 250-3S0 F. in vessel 19. After contact between the caustic and benzene has taken place the two layers sepa- States Patent F rate by gravity settling into a lower caustic layer and an upper benzene layer.

The lower caustic layer is withdrawn from vessel 19 by means of line 18 and added to the benzene flowing through line 1'7 as previously described. The strength of the caustic is maintained within the desired limits by discarding suitable amounts through outlet line 21 and adding additional make-up caustic through inlet line 22. In general, sutficient heat is provided by passing the benzene through heat exchanger 16 but if necessary other heating means may be provided either in vessel 19 or in line 18 to maintain the contacting benzene and caustic within the temperature range of 250 350 F. From vessel 19 the caustic treated benzene is withdrawn through line 23 and passed to a distillation step carried out in tower 24.

Tower 24 is provided with a side stream line 25 for removing a high purity benzene fraction and an outlet line 26 for removing an overhead fraction consisting of water vapors and benzene vapors. This overhead fraction is passed through condenser 27 and then through line 28 to a settler drum 29 in which a water layer and a hydrocarbon layer form. The water layer together with a portion of the hydrocarbon layer is withdrawn through outlet line 30 and discarded from the system and the remainder of the hydrocarbon layer recycled as reflux through line 31 to the top of distillation tower 2d. The bottom of the tower is provided with an outlet line 32 which discharges to a heat exchanger 33. As the bottoms pass via line 32 to heat exchanger 33, a high boiling flux oil is added thereto through inlet line 34. It is essential that the flux oil have a true boiling initial boiling point no more than 70 F. above benzene and not more than a 100 boiling range. A preferred true boiling initial boiling point for the flux oil is in the range of 200250 F. It is preferred to add the high boiling flux oil in an amount within the range of 2-10% of the charge volume of the benzene. From heat exchanger 33 a bottoms fraction is removed through outlet line 35 and a vapor fraction is returned to tower 2d through line 36.

In order to illustrate further the practice of the present invention, the following specific example is given:

Example A crude benzene feed stock obtained from phenol extractive distillation of a mixture of steam cracked and other low concentration benzene streams consisted of approximately benzene, 5% parafiins and 4.5% olefinic material of substantially the same boiling point as benzene. The crude benzene feed stock was treated with 30 pounds of 98% sulfuric acid per barrel of feed stock with subsequent settling and removal of acid sludge. The acid treated benzene was then treated by contacting it with 20 56. NaOH at a temperature of approximately 265 F. in a drum which provided 30 minutes residence time. From the settling drum an aqueous layer was withdrawn and discarded and a predominantly hydro carbon layer withdrawn from the top of the drum. T his hydrocarbon layer contained dissolved water in an amount of approximately 1%, hydrocarbons higher boiling than benzenes in an amount of approximately 2% and a minor portion of sulfur containing compounds. This material was discharged to a distillation column operating at a pressure less than 2 atmospheres absolute and to the lower part of the column fiux oil was added at the rate of 5 volume per cent of the benzene charge rate. A bettoms was Withdrawn from the column which contained approximately 1% of benzene based on the charge. An overhead stream consisting of substantially all of the water contained in the charge and approximately 4% benzene based on the charge was withdrawn from a reflux accumulator drum and settled into a heavier water containing layer and a lighter hydrocarbon layer. The hydrocarbon layer was returned for further treatment to the phenol extractive distillation unit from which the crude benzene feed stock was originally obtained. Reflux was supplied to the tower from the reflux accumulator. The benzene fraction was withdrawn as a side stream above the feed plate of the distillation tower and had a purity of 99.8% with a recovery based on the benzene charged to the column of about 95%.

It is to be emphasized that the steps of caustic washing and distillation must be carried out as described in order to obtain the high purity benzene product in accordance with the present invention. By way of explanation, it may be stated that as a result of the acid treating step the acid treated benzene contains acidic compounds such as benzene sulfonic acid esters and in addition substantially neutral sulfur containing compounds which are substantially water insoluble but benzene soluble such as sulfones and other neutral sulfur containing compounds. By contacting these materials with an alkali metal hydroxide at a temperature in the range of 250300 F. for at least 20 minutes and in the liquid phase there is not only a reaction between the alkali metal hydroxide and the acidic compounds but in addition the major portion of the sulfones and other neutral sulfur containing compounds hydrolyze and yield caustic soluble compounds. Thus, only a small amount of sulfur containing compounds are in the material sent to the distillation zone. In the distillation zone the introduction of a flux oil, higher boiling than the benzene so that it will remain in the bottoms, allows the withdrawal of alkylated benzene impurities, which have a boiling range of approximately 375 to 400 F. as well as sulfones and other neutral sulfur containing compounds. If these materials had a longer residence time in the distillation column they would decompose and form S02 and hydrocarbons lower boiling than benzene. As is well known, S02 is undesirable not only from the standpoint of causing acid wash color degradation of the benzene product but also because of its extreme corrosiveness to steel in the presence of water. These difficulties are avoided as explained by the use of high boiling flux oil in the bottom of the tower. It is also essential that an overhead be Withdrawn in order to obtain a benzene product substantially free from water vapors. Thus, the several steps of the process are essential in order to obtain a high purity benzene product.

Having fully described and illustrated the practice of the present invention, what I desire to claim and secure by Letters Patent is:

1. A method for finishing a crude benzene feed stock comprising approximately 95% benzene and substantially all of the remainder olefinic material of substantially the same boiling point as benzene, including the steps of contacting the crude benzene with strong sulfuric acid to form an acid sludge, separating said acid sludge therefrom, thereafter intimately contacting the acid treated benzene as a liquid with alkali metal hydroxide having a molarity within the range of 1 to 10 at a temperature within the range of 250350 F. for at least 20 minutes, separating the caustic solution from the caustic treated benzene and distilling the caustic treated benzene in a distillation zone to which a flux oil having a true initial boiling point no more than F. above said benzene and no more than 100 F. boiling range has been added in an amount in the range between 2% and 10% of the crude benzene feed stock, a small overhead fraction containing water vapors, a bottoms fraction consisting of said flux oil containing contaminants higher boiling than benzene and a distillate stream containing a high purity benzene is withdrawn as product.

2. A method for treating a crude benzene feed stock comprising approximately benzene, 4.5% olefinic material of substantially the same boiling point as benzene and the balance paratfins including the steps of contacting the feed stock with approximately 30 pounds of 98% sulfuric acid per barrel of feed stock to form an acid sludge, settling and removing of resultant acid sludge,

rate, withdrawing as overhead approximately 4% of the charge, withdrawing a bottoms fraction consisting of said flux oil containing contaminants higher boiling than benzene and withdrawing as a side stream benzene of a purity of substantially 99.8%.

3. A method in accordance with claim 2 in which the flux oil has an initial boiling point in the range of 200- 250 F. and is introduced near the bottom of the distillation zone in an amount of approximately 5% of the charge volume.

References Cited in the file of this patent UNITED STATES PATENTS 2,228,431 Archibald et al. Ian. 14, 1941 2,400,373 Schutze May 14, 1946 2,481,816 Browder et al. Sept. 13, 1949 2,597,427 Ayers et al. May 20, 1952- 2,649,404 Reynolds Aug. 18, 1953 OTHER REFERENCES Whitehead: Benzol D. Van Nostrand C0., 8 Warren St, New York, N. Y., (1920), pages 157-459. 

1. A METHOD FOR FINISHING A CRUDE BENZENE FEED STOCK COMPRISING APPROXIMATELY 95% BENZENE AND SUBSTANTIALLY ALL OF THE REMAINDER OLEFINIC MATERIAL OF SUBSTANTIALLY THE SAMD BOILING POINT AS BENZENE WITH STRONG SULFURIC ACID TO CONTACTING THE CRUDE BENZENE WITH STRONG SULFURIC ACID TO FORM AN ACID SLUDGE, SEPARATING SAID ACID SLUDGE THEREFROM, THEREAFTER INTIMATELY CONTACTING THE ACID TREATED BENZENE AS A LIQUID WITH ALKALI METAL HYDROXIDE HAVING A MOLARITY WITHIN THE RANGE OF 1 TO 10 AT A TEMPERATURE WITHIN THE RANGE OF 250*-350* F. FOR AT LEAST 20 MINUTES, SEPARATING THE CAUSTIC SOLUTION FROM THE CAUSTIC TREATED BENZENE AND DISTILLING THE CAUSTIC TREATED BENZENE IN A DISTILLATION ZONE TO WHICH A FLUX OIL HAVING A TRUE INITIAL BOILING POINT NO MORE THAN 70* F. ABOVE SAID BENZENE AND NO MORE THAN 100* F. BOILING RANGE HAS BEEN ADDED IN AN AMOUNT IN THE RANGE BETWEEN 2% AND 10% OF THE CRUDE BENZENE FEED STOCK, A SMALL OVERHEAD FRACTION CONTAINING WATER VAPORS, A BOTTOMS FRACTION CONSISTING OF SAID FLUX OIL CONTAINING CONTAMINANTS HIGHER BOILING THAN BENZENE AND A DISTILLATE STREAM CONTAINING A HIGH PURITY BENZENE IS WITHDRAWN AS PRODUCT. 